Preparation And Properties Of Fluorinated Polyacrylate/Waterborne Epoxy Resin Composite Coatings

Waterborne epoxy resin coatings have been widely used in rail transit field due to its advantages of convenient processing and low VOC emission.However,compared with solvent-based coatings,the performance of waterborne coatings has obvious deficiencies in terms of mechanical properties,wear resistance and corrosion resistance,which leads to their limited application under complex and harsh working conditions.These deficiencies are caused by poor dispersion of the emulsion in an aqueous environment and slow evaporation of water during the curing process,which increase the defects of the coating and decrease its density.In recent years,the modification of waterborne epoxy resin has been studied deeply by researchers.Among them,polymer blending and filler modification have become the current research hotspots and are effective methods to improve the performance.At present,the key of the two modification methods is to select appropriate blends and improve their compatibility and dispersion with coatings through specific functionalization modification.In this thesis,fluorinated polyacrylate composite latex particles containing epoxy resin were prepared by emulsion polymerization.It was blended with epoxy resin to prepare a fluorinated polyacrylate/epoxy resin composite coating with polymer interpenetrating network（IPN）structure,which was used as the coating matrix for subsequent research.In order to further improve the mechanical properties and wear resistance of composite coatings,graphite（Gr）and carbon nanotubes（CNTs）were selected as the reinforcing fillers.Fluorination treatment and polydopamine（PDA）were used for surface modification to prepare modified filler.Graphene oxide（GO）was selected to improve the barrier effect of composite coatings on corrosive media.Polypyrrole（Ppy）and cerium ions(Ce³⁺)were introduced as corrosion inhibitors,GO modified fillers carrying both of them were prepared to improve the corrosion resistance of composite coatings.The prepared composite coating has significant improvement in mechanical properties,abrasion resistance and corrosion resistance,which provides a research direction for the preparation of waterborne coatings used under severe working conditions.In this thesis,the microscopic morphology,chemical composition and modification mechanism of the composite latex particles and modified fillers were studied by various test methods.The composite coatings were tested on the macroscopic properties.Meanwhile,molecular dynamics simulation（MD）was used to study the microscopic mechanism of composite coating performance improvement.The main conclusions drawn from the thesis are as follows:（1）The epoxy resin in the fluorinated polyacrylate latex particles play a bridging role in the preparation of composite coatings,which solve the problem of poor compatibility between fluorine-containing components and waterborne epoxy resins.The dense IPN structure is formed by the forced mutual dissolution of polymer and matrix molecular chains.The storage modulus and damping performance of the composite coating are increased by 33.2%and 26.8%,respectively.The wear volume is reduced by 50.6%.The low-frequency impedance of the composite coating is increased by 3.4 times,and the diffusion coefficients of O₂ and Cl^-are obtained by molecular dynamics simulation,which decrease by 41.2%and 48.2%,respectively.The corrosion resistance of the coating has been significantly improved.（2）The agglomeration of modified Gr and CNTs fillers are obviously weakened due to the enhancement of the interaction with the matrix by surface amination or fluoridation.The mechanical properties and wear resistance of the composite coatings are significantly improved due to their excellent dispersion.PDA has the best modification effect.When the amount of Gr-PDA was 1 wt%and the amount of CNTs-PDA was 0.5 wt%,the energy storage modulus of the composite coatings can reach more than 40%.Gr fillers could destroy the wear resistance of composite coatings,while CNTs fillers can effectively improve it.Molecular dynamics simulation results show that the relative slippage between layer and layer of Gr fillers under the action of tangential stress leads to a large number of molecular chain migration in the matrix and poor wear resistance.For CNTs fillers,the rivet effect makes the molecular chain more difficult to fall off,and the wear resistance of the coating is significantly improved.（3）Ppy and Ce³⁺play a corrosion inhibition effect together by promoting the formation of a protective film.GO can increase the Diffusion path of corrosive media and enhance the barrier effect.Due to its excellent water solubility,it can drive the loaded corrosion inhibitor to achieve uniform dispersion,which is beneficial to the formation of a uniform passivation layer on the surface of the substrate.Modified fillers can significantly improve the corrosion performance of composite coatings,and the low-frequency impedance of them can be increased by one to two orders of magnitude.